In order to avoid tearing up a street whenever the flow of water or other liquids or gases through large main lines needs to be adjusted, stopcocks, commonly known as gate valves, are placed at strategic intervals in the lines and tubular service boxes are positioned above the valves to provide access from the street level. A long rod typically having a forked tool end may be used to actuate the valve from the street through the service box. These boxes may be anywhere from three inches to twelve inches in diameter. In order to protect the valve and also passers-by, a lid is placed at the top opening of the service box. Typical lids are made of cast iron and simply dropped into the tapered upper opening of the service box.
There may be hundreds of such gate valves and associated service boxes distributed around particular city. In most cases, the lids are held within the service box openings by gravity, rather than with any retaining structure, in order to save installation and service labor costs due to the great numbers of valves. Moreover, there are several inherent problems with providing a locking structure to the lid, as will be described below.
Although it is preferred to simply drop the lid into the top end of the service box, the lids frequently are displaced by passing vehicles. In a common occurrence, the front tire of a large truck cants the lid within the service box, after which the rear tire completely flips the lid out of the service box opening. With the lid removed, the valve is exposed, creating a danger of the main line being damaged. Also, the lid may crack due to its cast iron construction, thus requiring a replacement. Even more troublesome is the potential hazard caused by the flying lid and exposed hole to pedestrians and motorists alike. These problems are generally common to lids of 12" diameter or less, the larger lids having sufficient weight to resist being flipped.
Due to the aforementioned problems, and in some instances, to prevent tampering, there have been numerous designs to retain the lid in place over the service box. One such locking structure simply provides a thread on the exterior rim of the lid which mates with a female thread on the interior of the top end of the service box. Typically, the lid requires approximately half a turn to tighten onto the service box. It has been found, however, that repeated vibration from passing vehicle tires causes the lid to eventually loosen and be susceptible to displacement.
In another locking structure, a central nut in the lid actuates one or more outwardly extending fingers underneath the lid which interfere with some type of rim or flange fixed in the service box. While this is a slightly more advanced design, the nut tends to come loose, nevertheless. Furthermore, the nuts used in these lids have been of a special type requiring a five-sided tool to actuate. These tools and nuts are more costly than conventional ones, which is a major consideration for such a low-tech application, making them unsuitable for many municipalities or districts looking for cost-saving options. Furthermore, a maintenance worker must be in possession of the five-sided tool in order to obtain access to the gate valve. If the tool is lost or misplaced, maintenance work may be delayed.
An arrangement for threadingly mounting a lid over a tubular extension from a valve is shown in U.S. Pat. No. 2,344,893, issued to Montgomery. Another quite complex locking arrangement for a similar application is shown in U.S. Pat. No. 4,461,597, issued to Laurin. These and other designs drawn to locking lids for service boxes are either less than reliable or too complex for the cost-sensitive application.
Another drawback with prior service box lid designs is the absence of structure to compensate for misalignment between an upper level of the service box depending from street level and a lower section of the service box, which is centered over the gate valve. In the construction of such water main gate valves, the lower section of the service box is embedded in the fill of the roadway prior to the upper section being installed. The upper section comprises a larger diameter tube which fits over the lower section, but may not be exactly aligned therewith.
One illustrative street service box is shown in U.S. Pat. No. 1,032,503, issued to Rapp, and includes a set screw G which may be used to adjust the height of an upper casting relative to a lower pipe extending down to the valve. The design has the disadvantage that the set screw G is not accessible once the service box is in place. Therefore, any subsequent misalignment which occurs after placement cannot be corrected.
Due to the drawbacks of prior designs, there is a need for an improved gate valve lid which is inexpensive, simple to install and reduces the chance of displacement.